[jaycalgary]

I have a pair of Lambda pro's that get very little use with Lambda sig's around. Again I am looking at the Sigma for their panoramic sound. I was looking  at buying a pair but they
are not easy to find. I was running through Ideas to recreate the Sigma housing. So far my idea is to make a skeleton frame  the same or really close dimensions to the original 
using wood from a hobby store they make RC airplanes from. The Lambda pro drivers would be left on the aluminum plate and mounted in reverse to the wood skeleton.
The earpad side would be model plywood cut for the earpad opening and mounted to the wood skeleton. All other sides would have quarter inch square wire mesh and lined with
acoustic insulation same as original Sigma.
 
The idea is that the box of the original Sigma is not really all that sturdy and all the louvered plastic does not have to be there. It's the acoustic insulation on the inside that counts?
I think the idea of keeping the the drivers on the aluminum plate will be stiffer than the original and probably help the bass. Anyone think it is worth a shot or have any input?

 

[edstrelow]

Good luck with this project.  I don't think that the the louvered plastic grill on the Sigmas matter that much other than to try to keep the earcups rigid and to provide support for the mineral wool .
 
 I did an experiment which you can easily repeat, of running Lambda drivers without an enclosure, i.e. place them at 90 degrees to the ear in the position they would occupy if ther were mounted in a Sigma enclosure.  You get very poor sound, virtually no bass at all, so evidently the mineral wool is important.  However, when I went back to a real Sigma and sealed the enclosures with tape, I got a very boomy, echoey sound.  So evidently the mineral wool was pretty well chosen by the original Stax designer.  If you don't have enough seal of the box, you get no bass, but too much and the sound is echoey and boomy.
 
I am not sure what type wood you are considering.   I wouldn't think that balsa wood would be stiff enough though, but I could be wrong.

 

[jaycalgary]

Could someone with a pair of Sigmas take a few measurements to tell me how close my outside measurements are to a real pair of Sigmas? I would really appreciate it and thank you kindly if you would.
I posted a picture if it does not show clearly and someone is willing to confirm my measurements I will and take a more clear one. I think I have some really good ideas now and will be interesting to see how
this project turns out. There won't be wood though on this one. Here is a picture of the measurements I got from pictures of Sigmas on the web. I am guessing Sigmas are symmetrical?
 
1= 75mm "Earpad side"
2= 44mm "Rear short side"
3= 75mm "Opposite earpad side"
4= 78mm "Driver side"
 

 
So far the construction of the housing is going really good. I think I will have most of the housing built tomorrow. I ran into some problems with the lambda pro drivers. I removed them from the aluminum baffle. I took off 2 plastic oval rings that has mesh sandwiched between. Under them was a metal oval ring that holds the dust cover. The problem is it separated a little on one end for a few moments I have it sealed Ok temporarily.  Can a driver survive this? The dust cover is not broke but some air must have made its way in there. I will try to glue use some 2 part epoxy and go around the driver to make sure it is closed. They only used a few dabs around the whole driver. Maybe this is why is lot of older Stax have channel imbalances? Over time some air gets in and hurts the stator plates?I am going to try lightly epoxying the side with cheese cloth around the edge so then I can 2 way tape it to the aluminum baffle. One thing that is scary is the wire terminals especially the middle terminal. I am going to have to unsolder and bend it back as far as possible and solder the wire back on at the very end. It is still just going to barely clear hitting the aluminum baffle. Will a couple layers of high voltage tape in between be Ok? So far I think the housing boxes are coming out so good that may try 407 drivers in them in the future. I will put up a picture tomorrow if anyone cares to see.

 

[jjinh]

Hi jay. Sounds like an interesting project!
 
If no-one's posted measurements by the time I get home from work I'll do some measuring for you.

 

[jjinh]

Back with some measurements. It's actually not symmetrical. I hope you find this useful:
 

 

[jaycalgary]

Thank you. I can make some arcs with a compass and I will have the same shape. The rear measurement looks like 40mm  am not misreading and it is 48mm. Besides the drivers the project is coming along really good. I will post a picture in a day or two but so far it is coming out really well. Part of the Lambda pro housing recycled and mixed in.

 

[edstrelow]

Quote:

Could someone with a pair of Sigmas take a few measurements to tell me how close my outside measurements are to a real pair of Sigmas? I would really appreciate it and thank you kindly if you would.
I posted a picture if it does not show clearly and someone is willing to confirm my measurements I will and take a more clear one. I think I have some really good ideas now and will be interesting to see how
this project turns out. There won't be wood though on this one. Here is a picture of the measurements I got from pictures of Sigmas on the web. I am guessing Sigmas are symmetrical?
 
1= 75mm "Earpad side"
2= 44mm "Rear short side"
3= 75mm "Opposite earpad side"
4= 78mm "Driver side"
 

 
So far the construction of the housing is going really good. I think I will have most of the housing built tomorrow. I ran into some problems with the lambda pro drivers. I removed them from the aluminum baffle. I took off 2 plastic oval rings that has mesh sandwiched between. Under them was a metal oval ring that holds the dust cover. The problem is it separated a little on one end for a few moments I have it sealed Ok temporarily.  Can a driver survive this? The dust cover is not broke but some air must have made its way in there. I will try to glue use some 2 part epoxy and go around the driver to make sure it is closed. They only used a few dabs around the whole driver. Maybe this is why is lot of older Stax have channel imbalances? Over time some air gets in and hurts the stator plates?I am going to try lightly epoxying the side with cheese cloth around the edge so then I can 2 way tape it to the aluminum baffle. One thing that is scary is the wire terminals especially the middle terminal. I am going to have to unsolder and bend it back as far as possible and solder the wire back on at the very end. It is still just going to barely clear hitting the aluminum baffle. Will a couple layers of high voltage tape in between be Ok? So far I think the housing boxes are coming out so good that may try 407 drivers in them in the future. I will put up a picture tomorrow if anyone cares to see.

I don't think the drivers need be air-tight.  I am not sure if all Stax even have dust covers.  I have taken apart my 003's and didn't find any. 

 

[jjinh]

Quote:

Thank you. I can make some arcs with a compass and I will have the same shape. The rear measurement looks like 40mm  am not misreading and it is 48mm. Besides the drivers the project is coming along really good. I will post a picture in a day or two but so far it is coming out really well. Part of the Lambda pro housing recycled and mixed in.

It is indeed 40mm.

 

[jaycalgary]

Here is an picture of what I have going on so far. Some of it will be changed like the plexiglass behind the earpad. Wrong material to use. I am going to get model birch plywood for that piece.
I am happy to know the angle the driver is to the earpad thanks. The rest will be formed out of welded hardware mesh and the rest is up to the insulation. I am thinking of making one change
to the shape and that is to round out the back corner. Anyone think that could be a bad idea?
 

 
Here is an idea the kind of shape I am going for.
 

 

[chinsettawong]

I don't think it's a bad idea.

 

[Faust2D]

Cool project. Magnesium or aluminum frame would be better than wood, so would be some kind of polymer. But I guess wood is simpler to work with. Round corner would not be a bad, bit make sure you use mineral wool inside the cups since without it sigma sounds like crap.

 

[padam]

Interesting project, good luck with it.
 
Jazz's custom electrostats also look very interesting, cross between Lambdas and Sigmas: http://www.head-fi.org/forum/thread/417442/homemade-headphones#post_5569467

 

[edstrelow]

Quote:

Interesting project, good luck with it.
 
Jazz's custom electrostats also look very interesting, cross between Lambdas and Sigmas: http://www.head-fi.org/forum/thread/417442/homemade-headphones#post_5569467

Interesting project.  I regret that Stax abandoned the Sigma experiment many years ago.  I would think that it would be possible to build a better Sigma-type phone, with some variation in the design, as the referenced project tried to do.  The Lambda drivers still are a good start for such designs but it would be great to use something like the 007 or C32.  However because these drivers are round it could be difficult to make an enclosure which wouldn't be excessively bulky.

 

[jaycalgary]

"Jazz's custom electrostats also look very interesting, cross between Lambdas and Sigmas: http://www.head-fi.org/forum/thread/417442/homemade-headphones#post_5569467 "
 I am really glad to see these again I probably would have never found the thread.

 

[edstrelow]

 Stax introduced the Lambdas after the Sigmas and pitched them as Semi-Panoramic, claiming you would get some of the spatial projection benefits of the Sigma.  I can't say the Lambdas ever sounded any diferent in spatial qualities than most other stat phones, such as the Koss ESP950.